DIAGNOSIS OF CANCER

Malignant transformation of cells into cancer arises due to long term accumulation of genetic and epigenetic events. Early diagnosis of these transformations in cells can improve the prognosis of cancer cases. Cancer screening and surveillance methods include immuno histochemistry, in situ hybridization (FISH), flow cytometry and microarray are used nowadays for diagnosis. Microarray technology is a new and efficient approach to extract data of biomedical relevance for a wide range of applications. In cancer research, it will provide high-throughput and valuable insights into differences in an individual’s tumor as compared with constitutional DNA, mRNA expression, and protein expression and activity. This review highlights the recent developments in cancer diagnostic technologies and describes the eventual use of these technologies for clinical and research applications.

der to identify any variations from the normal si ze, feel, and texture of the organ or tissue.Different methods are used for the diagnosis of cancer those are

Histological Methods
These methods are based on microscopic examination of properly fixed tissues ,supported with complete clinical and investigative data.These methods are most valuable in arriving at the accurate diagnosis.These diagnosis by either of these methods is made on the basis of that cytological features of benign tumours resemble those of normal tissues and that they are unable to invade and metastasise,while malignant tumours are identified by lack of differentiation in cancer cell termed an aplasia( a condition whereby cells lose the morphological characteristics of mature cells and their orientation with respect to each other and to endothelial cells.)orcellular atypia(itis a pathologic term for a structural abnormality in a cell) and may invade as well as metastasis.

Cytological Methods
These methods for diagnosis consist of study of cells shed off into body cavities and study of cell by putting a fine needle introduced under vacuum into the lesion(fine needle aspiration cytology FNAC).

Fine Needle Aspiration Cytology
Fine Needle Aspiration Cytology (FNAC) is a diagnostic procedure where a needle is inserted into your body, and a small amount of tissue is sucked out for examination under a microscope.It is a quicker and less painful procedure than a Biopsy, but doctors still prefer a biopsy for lymphomas as it gives surer results.

Application
This type of sampling is performed for one of two reasons 1.
A biopsy is performed on a lump or a tissue mass when its nature is in question.

2.
For known tumors, this biopsy is performed to assess the effect of treatment or to obtain tissue for special studies.When the lump can be felt, the biopsy is usually performed by a Cytopathologisticor a Surgeon.In this case, the procedure is usually short and simple.Otherwise, it may be performed by an interventional radiologistic, a doctor with training in performing such biopsies under X-ray or ultrasoundguidance.In this case, the procedure may require more extensive preparation and take more time to perform.Also, fine-needle aspiration is the main method used for chorionic villus sampling as well as for many types of body fluid sampling, as shown in Fig 1and Fig 2.

Histochemistry and Cytochemistry
These are additional diagnosis tools which helps the pathologist in identifying the chemical composition of cell.Their constituents and their products by special staining methods.Though immunohistochemical techniques are more useful for tumourdiagnosis, histochemical and cytochemical methods are still employed for this purpose.

Immunohistochemistry
This is an immunological method of recognizing a cell by one or more of its specific components in the cytoplasm,cell membrane or nucleus .These cell components are combine with specific antibodies on the formaline fixed paraffinesection.thecomplex of antigen and antibody on the slide is made visible for light microscopic identification by either fluorescent dyes or by enzymes, as shown in Fig 3 .The list of immunochemical stains is ever increasing; one important group of such antibody stains is directed against various classes ofintermediate filaments which is useful in classification of poorly-differentiated tumours of epithelial or mesenchymal origin.list of tumours and stains are shown in Table 1.

Electron Microscopy
Ultra structural examination of tumour call offers selective role in diagnostic pathology 1.Cell junctions-their presence and type.2.Cell surface eg: presence of microvilli.3. Cell shape and cytoplasmic extinction.4.Shape of the nucleus and features of nuclear memberane.5. nucleoli-size and density.In marine biology, the abundance and distribution of photosynthetic plankton can be analysed.Size of particals is 1-50micron size.Flow cytometry can also be used in the field of protein engineering, to help identify cell surface protein variants.This is a computerized technique by which the detailed characteristics of individual tumour cell are recognized and quantified and the data can be stored for subsequent comparison too.

In Situ Hybridization
This is a molecular technique by which nucleic acid sequences can be localized by specifically labeled nucleic acid probe directly in the intact cell rather than by DNA extraction.It is shown in Fig 6.

Molecular Diagnostic Technique:
The group of molecular biologic methods in the tumour diagnostic laboratory are a variety of DNA/RNA-based molecular technique in which the DNA/RNA are extracted from the cell and then analysed.themolecular methods in tumour diagnosis can be applied in hematologic as well as non-hematologic malignancies by -Analysis of molecular cytogenetic abnormalities.
-Antigen receptor gene rearrangement and -By study of the oncogenic viruses at molecular level.

DNA Microarray Analysis of Tumours
Currently, it is possible to perform molecular profiling of a tumour by use of gene chip technology which allows measurement of level of expression of several thousand genes simultaneously.
The core principle behind microarrays is hybridization between two DNA strands, the property of complementary nucleic acid sequences to specifically pair with each other by forming hydrogen bonds between complementary nucleotide.A high number of complementary base pairs in a nucleotide sequence mean tighter non-covalent bonding between the two strands.After washing off non-specific bonding sequences, only strongly paired strands will remain hybridized.Fluorescently labeled target sequences that bind to a probe sequence generate a signal that depends on the hybridization conditions (such as temperature), and washing after hybridization.Total strength of the signal, from a spot (feature), depends upon the amount of target sample binding to the probes present on that spot.Microarrays use relative quantitation in which the intensity of a feature is compared to the intensity of the same feature under a different condition, and the identity of the feature is known by its position.It is observed in Fig 7,8.DNA microarray technology is a promising approach that allows both qualitative and quantitative screening for sequence variations in the genomic DNA of cancer cell.DNA microarray based samples.

Table 2 .
Most tumor markers are made by normal cells as well as by cancer cells; however, they are produced at much higher levels in cancerous conditions.These substances can be found in the blood, urine, stool, tumor tissue, or other tissues or bodily fluids of some patients with cancer.Most tumor markers are proteins.However, more recently, patterns of gene expressionand changes to DNA have also begun to be used as tumor markers.Markers of the latter type are assessed in tumor tissue specifically.Thus far, more than 20 different tumor markers have been characterized and are in clinical use.Some are associated with only one type of cancer, whereas others are associated with two or more cancer types.There is no "universal" tumor marker that can detect any type of cancer.Tumor markers are used to help detect, diagnose, and manage some types of cancer.Although an elevated level of a tumor marker may suggest the presence of cancer, this alone is not enough to diagnose cancer.Therefore, measurements of tumor markers are usually combined with other tests, such as biopsies, to diagnose cancer.A doctor takes a sample of tumor tissue or bodily fluid and sends it to a laboratory, where various methods are used to measure the level of the tumor marker.List of tumours markers for different cancers are listed in